1. Field of the Invention
This invention relates to heating units for use with a chafing dish and, more particularly, to an electric or gas-powered heating unit which is removably attached to extend below a water pan within the chafing dish.
2. Background of the Invention
A conventional chafing dish includes a frame holding a water tray and a food tray, with a system of complimentary flanges in the trays supporting the food tray to extend above the water tray. The water tray is heated by means of a heating unit burning a solid hydrocarbon fuel sold, for example, under the trade name STERNO, generally with the heater being supported on a structure forming a part of the frame. An example of this type chafing dish of is shown in U.S. Pat. No. Des. 318,976. While this kind of apparatus is widely used to keep food warm as it is presented at a buffet or party, several problems are associated with its use. First, the solid fuel, which is expensive, cannot easily be used to exhaustion, so partly used containers are typically discarded after use. In addition, chafing dishes are often used for outdoor events in which it is difficult to keep the heating units lit during windy conditions. Even when the heating units remain lit during windy conditions, the flame may be held away from the pan by the wind, so that heating is ineffective. At some events, such heaters cannot be used due to restrictions on the use of open flames. Additionally, it is often not apparent when the fire in a heating unit goes out, whether due to the wind or to the exhaustion of the fuel, so that the food is allowed to cool before the problem is discovered. Furthermore, it is often not apparent when the water within the water tray boils away, so that food is burned and the chafing dish is damaged by overheating before the problem is discovered. Finally, objections are often raised to the odor caused by burning the solid fuel.
Various of these problems may be solved by using a chafing dish heated by an electric heating element. Several examples from the patent literature describe food warmers including submerged electric heating elements extending within a water tray. For example, U.S. Pat. No. 4,658,117 describes a chafing dish having a stationary hollow housing extending within the water tray to define a cylindrical passage having an entrance through the outside of the tray. A removable member containing an electric resistance heater is inserted within the passage, with an electric cord extend outward. U.S. Pat. No. 5,381,729 describes a food warming vessel including a sump vessel partly filled with water, serving as the water tray in a chafing dish, with a U-shaped electric heating element held in place to extend within the water. The ends of the heating element are thermally connected through a metal bar to a thermostat used to control the heating element. U.S. Pat. No. 5,045,672 describes a chafing dish having a constantly energized, lift-out immersion heater including a first loop, positioned in the water pan and configured to permit concurrent use of flame beneath the water pan from cans of fuel without the flame damaging the heater. The heater also includes cool arms which extend upward through notches in the food pan or in the water pan. The water in the pan serves to moderate the temperature achieved during operation. U.S. Pat. No. 5,990,455 describes a chafing dish including a heating element forming a loop extending within the water of the water tray and extending upward to be supported by a rectangular frame extending along the upper flange of water tray. While each of these patents describes a chafing dish including an electric heating element, what is needed is a removable electric heating unit for use with existing, conventional chafing dishes in place of the canned fuel burners.
U.S. Pat. No. 6,157,007 describes an immersion heater, including a heating element forming a loop to extend within the water of the water tray of a chafing dish and additionally extending upward to be supported by a foldable L-shaped frame extending along two sides of the water tray. While such a heater can be used with a number of different chafing dishes, substantial limitations are placed on the geometry of the chafing dish. For example, the water tray must be large enough to include the loop of the heating element. If the water tray is too shallow, the loop of the heating element cannot fit within the tray. On the other hand, if the food tray extends too far down into the water tray, the food tray cannot be placed within the water tray with the heating element in place. What is needed is an attachable heating unit requiring only a water tray within the chafing dish having a sufficient flat area for the attachment of the heating element.
Additionally, removable immersion heaters having loop-type heating elements tend to be difficult to transport and store without damaging the exposed and unsupported heating elements. What is needed is a heating unit in which an electric element is mounted within a recessed plate to reduce its fragility.
U.S. Pat. No. 5,977,521 describes a chafing dish heated with an electric heater removably supported by a shelf disposed below the chafing dish. The base includes a base having a cylindrical bottom portion held within an aperture in the shelf sized for receiving a standard can heater. The heater further includes a resilient member extending upward from the base, and an electric heating assembly coupled to the resilient member opposite the base. The heating assembly has a heating surface positionable above the base by the compression of the resilient member. The heating surface is biased against the chafing dish when the base is supported by the shelf to provide a thermal interface to transfer heat between the heating surface and the chafing dish. What is needed is a simple method for holding an electrically heated heating surface against the lower surface of the water tray in a chafing dish without relying on a specific geometry of the chafing dish to include an appropriately spaced lower shelf with a circular aperture.
Chafing dishes are generally available in full-sized units requiring two standard can heaters or two of the electric heaters described in U.S. Pat. No. 5,977,521. Smaller chafing dishes requiring only one can heater or one of these electric heaters are also available. What is needed is a removable electric heater that cab be used as a single unit with either the larger type of chafing dish or with the smaller type of chafing dish.
U.S. Pat. No. 4,899,722 describes a burner assembly for use with a chafing dish supported above a support surface by a leg structure. The burner assembly includes a butane fuel source or reservoir, a burner head connected to the fuel source, a valve mounted between the fuel source and the burner head to control the flow of butane to the burner head, and a burner head support structure supporting the burner head above the support surface. The burner support structure further includes a base having a portion formed for positioning proximate and outwardly of the leg structure of the chafing dish, and an arm portion, holding the burner head, extending as a cantilever from the base portion to allow the placement of the burner head over a conventional shelf provided in the chafing dish to hold a canned fuel heater. Four vertically adjustable legs extend downward from the base portion, being adjusted to space the burner head at an appropriate distance below the lower surface of the water pan of the chafing dish. What is needed is a gas-powered burner assembly including a means holding the burner at the appropriate distance below the lower surface of the lower surface of the water pan without a need for leg adjustments and without the placement of a base portion outside the leg structure of the chafing dish.
The patent literature also includes a number of descriptions of devices including permanent magnets used to removably fasten the devices to structures composed of magnetic materials. For example, U.S. Pat. No. 4,506,138 describes the use of a preheater unit magnetically attachable the surface of an oil pan of an automobile engine, with magnetic flux extending from a permanent magnet within the unit through a pair of magnetic pole pieces and a non magnetic heat transfer plate to the magnetic attachment structure of the oil pan. For example, U.S. Pat. Nos. 5,405,004 and 5,699,910 describe tool trays having magnets for attachment to magnetic surfaces. U.S. Pat. No. 4,484,682 describes a container for food and miscellany having a permanent magnet in its bottom for holding the container in place on a magnetically attractable surface. U.S. Pat. No. 4,638,786 describes a utensil holder having magnets used for attachment of a magnetic cooking surface. U.S. Pat. No. 3,423,708 describes a crescent shaped magnetic sheet, with a pair of the plates, placed on opposite sides of a pan, being used to hold the pan in place on the magnetic surface of a stove. U.S. Pat. No. 4,867,410 describes a combination stand/holder having a channel-shaped column with a magnet and slots for receiving handles of utensils, which are held in place over a magnetic stove top surface. U.S. Pat. No. 4,492,355 describes a mounting device for a heater module which permits rapid installation and removal of the device from a ferromagnetic surface.
U.S. Pat. No. 2,507,559 describes a pair of cleaning elements provided with permanent magnets and adapted to be placed on opposite sides of a window pane or similar surface to be cleaned. When one cleaning element is rubbed against the inside surface of the pane, the magnetic field causes the other element to move correspondingly, so that both surfaces of the window pane may be cleaned simultaneously.
What is needed is a means for removably attaching a heating device to the nonmagnetic surface of a conventional chafing dish water tray.
According to a first aspect of the invention, a heating unit and an attachment frame are provided for heating a chafing dish. The heating unit includes a first magnetic attachment structure having a first face extending upward, a first frame attached to the first magnetic attachment structure to extend downward from the first face, and a heating element for generating heat within the first frame. The attachment frame includes a second magnetic attachment structure having a second face extending downward, wherein the first face of the first magnetic attachment structure is magnetically attracted to the second face of the second magnetic attachment structure.
Preferably, the first magnetic attachment structure includes a number of first magnetic attachment devices attached to the first frame in a first pattern, and the second magnetic attachment structure includes a plurality of second magnetic attachment devices attached to the second frame, in a pattern aligning the second magnetic attachment devices with the first magnetic attachment devices in the first pattern. Each of these first magnetic attachment devices includes a first device face extending along the first face, and each of these second magnetic attachment devices includes a second device face extending along the second face. The first device face of each of the first magnetic attachment devices is magnetically attracted to a second device face of an adjacent second magnetic attachment device among the second magnetic attachment devices.
The heating element may include an electric resistance-heating element, with the heating unit additionally including a line cord for supplying electrical current to the heating element. Alternately, the heating element may include a gas burner, with the heating unit additionally including a gas line for supplying combustible gas to the gas burner.
In accordance with another aspect of the invention apparatus for heating food is provided. The apparatus includes a food tray for holding the food, a water tray for holding water extending below the food tray, a heating unit, and an attachment frame. The water tray includes a flat lower portion composed of a nonmagnetic material. The heating unit includes a first magnetic attachment structure having a first face extending upward, a first frame attached to the first magnetic attachment structure to extend downward from the first face, and a heating element for generating heat within the first frame. The attachment frame, which is disposed on top of the flat lower portion of the water tray includes a second magnetic attachment structure having a second face extending downward, and wherein the heating unit is held in place under the flat lower portion of the water tray by magnetic attraction between the first and second magnetic attachment structures.